Apparatus for deterioration diagnosis of an oxidizing catalyst

ABSTRACT

An unburned fuel supply section performs temperature rise control to supply fuel to an oxidizing catalyst disposed upstream of an exhaust purification device to cause temperature rise of the exhaust purification device using heat generated in oxidation reaction of fuel on the catalyst. During the temperature rise control, an actual cumulative fuel quantity calculation section obtains actual cumulative fuel quantity by accumulating the amount of fuel supplied to the catalyst. A theoretical cumulative fuel quantity calculation section calculates fuel supply quantity required for temperature rise of the exhaust purification device on the premise that oxidation performance of the catalyst is not deteriorated, and obtains theoretical cumulative fuel quantity by accumulating the calculated fuel supply quantity. After the temperature rise control ends, a deterioration determination section determines whether the catalyst is deteriorated, on the basis of the ratio between the actual cumulative fuel quantity and the theoretical cumulative fuel quantity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an apparatus for deterioration diagnosis of an oxidizing catalyst, specifically an apparatus for deterioration diagnosis for determining deterioration of an oxidizing catalyst disposed upstream of an exhaust purification device of an engine to cause temperature rise of the exhaust purification device.

2. Description of the Related Art

In an exhaust system of, for example a diesel engine or a lean burn engine, there is provided an exhaust purification device, such as a diesel particulate filter (hereinafter abbreviated to DPF) for trapping particulate matter (hereinafter abbreviated to PM) in exhaust, or an adsorption-type NOx catalyst capable of adsorbing NOx (nitrogen oxides) in exhaust. On the DPF, forced regeneration for removing the trapped PM is performed appropriately, while on the NOx catalyst, NOx purge for releasing and reducing the adsorbed NOx is performed appropriately. Further, the adsorption-type NOx catalyst experiences so-called sulfur poisoning, which is a phenomenon that SOx (sulfur oxides) adsorbed in place of NOx lowers exhaust purification performance of the NOx catalyst. In some cases, SOx purge for removing the adsorbed SOx is performed as a measure against the sulfur poisoning.

Burning-off of PM by forced regeneration and removal of SOx by SOx purge require temperature rise of the DPF and the NOx catalyst to above a normal temperature range. Thus, the forced regeneration and the SOx purge are performed by supplying unburned fuel onto an oxidizing catalyst disposed upstream of the DPF and the NOx catalyst in the direction of the exhaust gas flow, and causing a temperature rise using heat generated in oxidation reaction of the unburned fuel on the oxidizing catalyst. Thus, the temperature rise of the DPF and the NOx catalyst depends on the oxidation performance of the oxidizing catalyst.

The oxidizing catalyst that is deteriorated or in some abnormal condition (hereinafter, the word “deteriorated” will be used to mean “deteriorated or in some abnormal condition”) cannot cause the temperature rise of the DPF and the catalytic NOx converter to a required level, resulting in insufficient forced regeneration and SOx purge. The DPF, the NOx catalyst and the like, not able to exhibit the intended performance for such reason cause a problem that harmful substances are emitted into the atmosphere. Thus, for example in North America, legal regulations concerning the OBD (on-board diagnosis) require that vehicles be equipped with an apparatus for deterioration diagnosis of an oxidizing catalyst. In order to comply with such legal regulations, etc., a variety of apparatuses for deterioration diagnosis have been proposed, one of which is disclosed in Japanese Unexamined Patent Publication 2005-48663 (hereinafter referred to as Patent Document 1), for example.

The apparatus for deterioration diagnosis in Patent Document 1 is directed to an oxidizing catalyst used for forced regeneration of the DPF. Specifically, if, during the forced regeneration, the state that the outlet temperature of the oxidizing catalyst (DPF inlet temperature) is lower than a target temperature required for burning-off of PM continues for a predetermined period of time, the apparatus for deterioration diagnosis determines that the oxidizing catalyst is deteriorated. Also, if the state that the amount of fuel supplied onto the oxidizing catalyst by post-injection is no less than a predetermined value continues for a predetermined period of time, the apparatus for deterioration diagnosis determines that the oxidizing catalyst is deteriorated.

The apparatus for deterioration diagnosis disclosed in Patent Document 1 has, however, the following problems:

The apparatus for deterioration diagnosis disclosed in Patent Document 1 determines whether or not the oxidizing catalyst is deteriorated on the basis of the temperature or the amount of fuel during forced regeneration. Thus, at the time that the deterioration is recognized, the oxidizing catalyst is already so deteriorated that the forced regeneration is difficult to continue. The discontinuation of the forced regeneration results in PM remaining in the DPF, so that exhaust purification performance, vehicle traveling performance, etc. begin to lower immediately after the deterioration is identified.

Further, the parameters which the apparatus for deterioration diagnosis disclosed in Patent Document 1 uses for the determination of deterioration include the outlet temperature of the oxidizing catalyst. The outlet temperature of the oxidizing catalyst, which should represent temperature rise caused by the oxidizing catalyst, is however influenced by environmental conditions such as outside air temperature, so that in some environmental conditions, the apparatus for deterioration diagnosis may erroneously determine that the oxidizing catalyst is deteriorated. Specifically, for example at very low temperatures of outside air, the outlet temperature of the oxidizing catalyst rises slowly, which causes problems such that the apparatus for deterioration diagnosis determines that the oxidizing catalyst is deteriorated, although it is actually not deteriorated, and leads the driver to unnecessary repair.

SUMMARY OF THE INVENTION

An aspect of the present invention is directed to an apparatus for deterioration diagnosis of an oxidizing catalyst, comprising; an exhaust purification device disposed in an exhaust passage of an engine for purifying exhaust from the engine; an oxidizing catalyst disposed upstream of the exhaust purification device; unburned fuel supply means for, when temperature rise of the exhaust purification device is required, performing temperature rise control to supply unburned fuel to the oxidizing catalyst to cause temperature rise of the exhaust purification device using heat generated in oxidation reaction of the unburned fuel on the oxidizing catalyst; actual cumulative fuel quantity calculation means for obtaining actual cumulative fuel quantity by successively accumulating the amount of unburned fuel supplied to the oxidizing catalyst by the unburned fuel supply means during the temperature rise control; theoretical cumulative fuel quantity calculation means for calculating fuel supply quantity required for temperature rise of the exhaust purification device, on the premise that oxidation performance of the oxidizing catalyst is not deteriorated, and obtaining theoretical cumulative fuel quantity by successively accumulating the calculated fuel supply quantity during the temperature rise control; and deterioration determination means for determining whether or not the oxidizing catalyst is deteriorated, on the basis of the ratio between the actual cumulative fuel quantity obtained by the actual cumulative fuel quantity calculation means and the theoretical cumulative fuel quantity obtained by the theoretical cumulative fuel quantity calculation means, after the temperature rise control ends.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus, are not limitative of the present invention, and wherein:

FIG. 1 is an overall structural view showing a diesel engine having an apparatus for deterioration diagnosis of an oxidizing catalyst according to an embodiment of the present invention; and

FIG. 2 is a flow chart showing a malfunction diagnosis routine executed by an ECU in the diesel engine shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings attached, an embodiment of the present invention will be described in detail.

FIG. 1 is an overall structural view showing a diesel engine (hereinafter referred to as “engine”) having an apparatus for deterioration diagnosis of an oxidizing catalyst according to an embodiment of the present invention. The engine 1 is an inline 6-cylinder engine, and a fuel injection valve 2 is provided for each cylinder. Pressurized fuel is supplied to the respective fuel injection valves 2 by means of a common rail 3, and each fuel injection valve 2 injects fuel into its associated cylinder when opened.

An intake manifold 4 for supplying intake air to the respective cylinders is connected to the intake side of the engine 1. An intake passage 5 connected to the intake manifold 4 includes an air flow sensor 8 for measuring intake air quantity Qa, a compressor 7 a of a turbocharger 7, and an intercooler 8 arranged in this order in the direction of the intake air flow.

An exhaust manifold 10 for emitting exhaust from the respective cylinders is connected to the exhaust side of the engine 1. At the outlet of the exhaust manifold 10, there is disposed a turbine 7 b of the turbocharger 7, mechanically linked with the compressor 7 a by a shared axis. An exhaust passage 11 is connected to the turbine 7 b. The exhaust passage 11 includes a catalytic converter 12 and a silencer not shown. The catalytic converter 12 is composed of an oxidizing catalyst 13 and a DPF 14 (exhaust purification device) located downstream of the oxidizing catalyst 13.

The oxidizing catalyst 13 is provided to cause oxidation reaction of unburned fuel, and comprises a ceramic honeycomb carrier and a catalyst layer carried on the carrier, where the catalyst layer is formed of a precious metal such as platinum (Pt).

The DPF 14 comprises a ceramic honeycomb body with a large number of exhaust paths formed axially. The exhaust paths are provided such that an upstream opening and a downstream opening of each of the exhaust paths are closed alternately. When exhaust is made to flow through porous walls defining the exhaust paths, PM (particulate matter) in the exhaust is trapped by the DPF 14.

The configuration of the exhaust system of the engine 1 is not restricted to this. For example, the exhaust system may include a NOx catalyst for converting NOx in exhaust, an oxidizing catalyst disposed downstream of the DPF 14, etc.

In the vehicle interior, an ECU (electronic control unit) 21 comprising input/output devices, memory units (ROM, RAM, etc.) for storing control programs, control maps, etc., a central processing unit (CPU), timer counters, etc., which are not shown, is installed.

To the input of the ECU 21, various sensors, including the air flow sensor 6, an inlet temperature sensor 22, and an outlet temperature sensor 23, are connected. The inlet temperature sensor 22 detects the temperature (inlet temperature Tin) of exhaust introduced to the oxidizing catalyst 13. The outlet temperature sensor 23 is disposed downstream of the oxidizing catalyst 13 and detects the temperature (outlet temperature Tout) of exhaust emitted from the oxidizing catalyst 13 (introduced to the DPF 14). To the output of the ECU 21, various devices, including the fuel injection valves 2 for the respective cylinders, and a warning lamp 24 provided near the driver's seat of the vehicle, are connected.

The ECU 21 sets target values for fuel injection quantity, injection timing, common rail pressure, etc., on the basis of detected information, such as a driver's accelerator depression amount, engine revolving speed, etc., and drives the engine 1 by performing drive-control of the fuel injection valves 2, adjustment of the common rail pressure, etc. on the basis of the target values.

While the engine 1 is operating, exhaust from the engine 1 flows through the exhaust manifold 10 to the exhaust passage 11, and through the oxidizing catalyst 13 to the DPF 14. As the exhaust flows through the walls of the paths of the DPF 14, PM contained in the exhaust is trapped on the walls, and then the exhaust is emitted into the atmosphere. The amount of PM trapped on the DPF 14 gradually increases. Thus, continuous regeneration of the DPF 14 is performed using, as an oxidizing agent, NO₂ produced in oxidation reaction of NO in exhaust, occurring on the oxidizing catalyst 13 disposed upstream of the DPF 14. Specifically, in a specified operating state of the engine 1 (for example, in an operating state with relatively high exhaust temperature), the PM trapped by the DPF 14 is continuously burned off, using the NO₂, as an oxidizing agent, supplied from the oxidizing catalyst 13.

If an engine operating state that does not produce such continuous regeneration effect on the DPF 14 continues, the amount of PM trapped and accumulated in the DPF 14 gradually increases and exceeds the allowable limit. In order to avoid such situation, the ECU 21 calculates the amount of PM trapped by the DPF 14 on the basis of the engine 1 operating state and accumulates the calculated amount, and performs forced regeneration of the DPF 14, namely forcedly burns off the PM in the DPF 14 before the cumulative PM quantity exceeds the allowable limit for the DPF 14. The manner of determining whether to perform forced regeneration is not restricted to this. For example, whether to perform forced regeneration can be determined on the basis of pressure difference across the DPF 14 (pressure loss in the DPF 14), which increases with an increase in PM trap quantity.

In the present embodiment, forced regeneration is performed using post-injection (so-called late post-injection). Specifically, unburned fuel is supplied to the oxidizing catalyst 13 by performing post-injection in expansion stroke or exhaust stroke after main injection. In the forced regeneration, heat generated in oxidation reaction of unburned fuel on the oxidizing catalyst 13 causes a temperature rise of the DPF 14 downstream of the oxidizing catalyst 13 to the target temperature (temperature allowing burning-off of PM, 650° C., for example), so that PM is burned off (unburned fuel supply means). It is to be noted that the ECU 21 estimates the bed temperature of the DPF 14 from the outlet temperature Tout detected by the outlet temperature sensor 23, and performs forced regeneration so that the bed temperature will become closer to the target temperature.

As clear from the above, rise in temperature of the DPF 14 in the forced regeneration depends on the oxidation performance of the oxidizing catalyst 13, and the deterioration of the oxidizing catalyst 13 immediately results in unsuccessful forced regeneration, and therefore, lowering in exhaust purification performance and vehicle traveling performance. Thus, in the present embodiment, the ECU 21 performs deterioration diagnosis of the oxidizing catalyst 13 in connection with the forced regeneration. Next, the details of the deterioration diagnosis of the oxidizing catalyst 13 will be described.

FIG. 2 is a flow chart showing a malfunction diagnosis routine executed by the ECU 21. The ECU 21 executes this routine at predetermined control intervals, while the ignition switch of the vehicle is in ON-position.

First, at Step S2, the ECU 21 determines whether the operating state of the engine 1 is in an operating region allowing correct malfunction diagnosis. Specifically, when the operating-state variables, such as fuel injection quantity for the engine 1, engine revolving speed, coolant temperature, ECR valve lift amount, time elapsed after start of the engine, post-injection (so-called early post-injection) quantity, namely the amount of fuel injected by post-injection performed immediately after main injection to burn off PM produced within the cylinders by the main injection, etc., are within their predetermined ranges and the sensors for detecting information used in deterioration diagnosis operate normally, the ECU 21 determines “Yes” at Step S2.

At next Step S4, the ECU 21 determines whether or not the engine 1 is now operating in forced-regeneration mode, and if the engine is in a normal operation mode other than the forced-regeneration mode, determines “No” at this step and finishes the routine. Broadly, there are two types of forced regeneration, namely automatic regeneration performed automatically during traveling, and manual regeneration caused by the driver manipulating an instruction button (not shown) near the driver's seat after parking the vehicle for forced regeneration. Although the details will be omitted, when the ECU 21 determines that forced regeneration is required from the PM trap quantity, etc., automatic regeneration is performed during traveling as long as it is possible. If, however, the DPF 14 has not experienced a sufficient temperature rise, for example because low-speed traveling has continued, the ECU 21 warns the driver to park the vehicle for manual regeneration, and then, in response to the driver's manipulation of the instruction button, performs manual regeneration while driving the engine 1 under the conditions optimal for raising the DPF temperature.

Whichever regeneration, automatic or manual, is being performed, the ECU 21 determines “Yes” at Step S4 above, namely determines that the engine is in forced-regeneration mode. Then, at next step S6, if it is determined that the conditions corresponding to the forced regeneration have continued for a predetermined period of time (3 sec, for example), the ECP 21 advances the procedure to Step S8. At Step 8, the EPC 21 calculates actual cumulative fuel quantity A for use in deterioration determination concerning the oxidizing catalyst 13 (actual cumulative fuel quantity calculation means). At next step S10, the EPC 21 calculates theoretical cumulative fuel quantity B also for use in deterioration determination (theoretical cumulative fuel quantity calculation means). Then at Step S12, the ECU 12 determines whether or not the forced regeneration has ended, and repeats processing at Steps S8 and S10 until it determines “Yes” at Step S12.

Processing at Step S8 is performed on the basis of actual post-injection quantity, namely the amount of fuel actually injected by post-injection (late post-injection) performed for the temperature rise to the target temperature in forced regeneration. The ECU 21 obtains the actual cumulative fuel quantity A by accumulating the actual post-injection quantity, successively. At Step 10, the ECU 21 calculates theoretical post-injection quantity, namely the amount of fuel required for the temperature rise to the target temperature, on the premise that the oxidation performance of the oxidizing catalyst 13 is not deteriorated (new, or unused), and obtains the theoretical cumulative fuel quantity B by accumulating the theoretical post-injection quantity, successively.

The oxidizing catalyst 13 not deteriorated exhibits the greatest possible oxidation performance, so that the unburned fuel supplied by post-injection is oxidized and contributes to the temperature rise of the DPF 14 with the highest possible efficiency. Thus, the theoretical post-injection quantity calculated on the basis of such situation is the smallest value for post-injection quantity required for the temperature rise of the DPF 14. On the other hand, the actual post-injection quantity controlled to achieve the temperature rise to the target temperature in actual forced regeneration is a value calculated corresponding to the oxidation performance that the oxidizing catalyst 13 is actually exhibiting. Decrease in oxidation performance due to deterioration of the oxidizing catalyst 13 leads to decrease in efficiency of raising the temperature of the DPF 14. The more the oxidizing catalyst 13 deteriorates, the greater amount of unburned fuel needs to be supplied to the oxidizing catalyst 13. Thus, the actual post-injection quantity increases as the oxidizing catalyst 13 deteriorates to a greater degree.

At the time that the forced generation has ended, the theoretical cumulative fuel quantity B obtained represents the total post-injection quantity required when the oxidizing catalyst 13 not deteriorated is used, while the actual cumulative fuel quantity A obtained is the total post-injection quantity actually consumed. When the oxidizing catalyst 13 is new and therefore not deteriorated, the actual cumulative fuel quantity A is equal to the theoretical cumulative fuel quantity B. When, however, the oxidizing catalyst 13 is deteriorated, greater degree of deterioration, therefore greater degree of lowering in oxidation performance of the oxidizing catalyst 13 results in greater plus-direction deviation of the actual cumulative fuel quantity A from the theoretical cumulative fuel quantity B.

The way that the temperature of the DPF 14 rises due to the heat generated in the oxidation reaction of unburned fuel on the oxidizing catalyst 13 depends on the inlet temperature of the oxidizing catalyst 13 and the flow rate of exhaust passing through the oxidizing catalyst 13. Thus, selecting the inlet temperature of the oxidizing catalyst 13 and the intake air flow rate (correlating with the exhaust flow rate) of the engine 1 as parameters, and determining the relation between these parameters and the required post-injection quantity, for each target temperature, by experiment using a new catalytic oxidizer 13, maps representing the relation for each target temperature are set in advance. At Step S10, the ECU 21 selects a map corresponding to the current target temperature in the forced regeneration, and the ECU 21 obtains a theoretical post-injection quantity corresponding to the inlet temperature Tin detected by the inlet temperature sensor 22 and the intake air quantity Qa detected by the air flow sensor 6, from the selected map.

At next Step S14, the ECU 21 determines whether or not the ratio between the actual cumulative fuel quantity A and the theoretical cumulative fuel quantity B exceeds a predetermined first threshold value α (1.5, for example) (deterioration determination means). Next, at Step S16, the ECU 21 determines whether or not the actual cumulative fuel quantity A exceeds a predetermined second threshold value β (40 mg, for example) (deterioration determination means). The amount of unburned fuel required for the temperature rise of the DPF 14 differs between the automatic regeneration performed during traveling and the manual regeneration performed while the vehicle is parked, which difference comes from wind caused by traveling, difference in exhaust flow rate, etc. Thus, for the first threshold value α and second threshold value β, different values are predetermined for the manual regeneration and the automatic regeneration. At Steps S14 and S16, the ECU 21 uses the threshold values α, β for deterioration determination, chosen according to the type of regeneration, manual or automatic. If the ECU 21 determines “No” at Step S14 or S16, the ECU 21 finishes the routine. If the ECU 21 determines “Yes” at both steps, the ECU 21 advances the procedure to Step S18 to put the warning lamp 24 on to urge the driver to repair.

The ratio between the actual cumulative fuel quantity A and the theoretical cumulative fuel quantity B and the actual cumulative fuel quantity A alone are each a value representing the deterioration of the oxidizing catalyst 13, definitely. However, while the actual cumulative fuel quantity A, i.e., the total post-injection quantity actually consumed varies depending on the situation in which the forced regeneration is performed, the ratio between the actual cumulative fuel quantity A and the theoretical cumulative fuel quantity B does not experience such variation. Thus, the use of the ratio between the actual cumulative fuel quantity A and the theoretical cumulative fuel quantity B can lead to a more appropriate deterioration determination. However, for example, as the DPF temperature becomes closer to the target temperature, the actual post-injection quantity and the theoretical post-injection quantity gradually becomes smaller (although the ratio does not change), which makes the ratio between the actual cumulative fuel quantity A and the theoretical cumulative fuel quantity B, used at Step S14, more likely to be influenced by error factors such as disturbance, and therefore leads to a lowered reliability. In view of this, the processing at Step S16 based on the actual cumulative fuel quantity A alone is also provided.

According to the above-described processing of the ECU 21, at the time of determining whether or not the oxidizing catalyst 13 is deteriorated, the forced regeneration of the DPF 14 has already ended. Accordingly, even if it is determined that the oxidizing catalyst 13 is deteriorated, it leads to no problems as long as measures such as repair of the catalytic oxidizer 13 are taken before forced regeneration is performed next time. Thus, unlike the apparatus for deterioration diagnosis disclosed in Patent Document 1 designed to determine the deterioration during forced regeneration, for example, the apparatus for deterioration diagnosis of the oxidizing catalyst 13 according to the present embodiment can prevent the problem that the forced regeneration of the DPF 14 is interrupted immediately after the recognition of the deterioration is made, causing lowering in exhaust purification performance and traveling performance.

Further, the actual cumulative fuel quantity A and the theoretical cumulative fuel quantity B used in deterioration determination are each the cumulative amount of unburned fuel supplied to the oxidizing catalyst 13, which is not influenced by environmental conditions such as outside air temperature. Thus, unlike the apparatus for deterioration diagnosis disclosed in Patent Document 1 designed to determine the deterioration on the basis of the outlet temperature of the oxidizing catalyst (which varies depending on the environmental conditions, even under the same oxidation performance of the oxidizing catalyst), for example, the apparatus for deterioration diagnosis according to the present embodiment can prevent the problem that the influence of the environmental conditions leads to determination error, and achieve a high accuracy of deterioration determination, removing the possibility of determination error.

Further, the apparatus for deterioration diagnosis according to the present embodiment is designed to calculate the theoretical post-injection quantity taking account of the inlet temperature Tin of the oxidizing catalyst 13 and the intake air flow rate Qa of the engine 1 which influence the way that the temperature of the DPF 14 rises. Thus, the apparatus for deterioration diagnosis according to the present embodiment can calculate the theoretical cumulative fuel quantity B accurately, which leads to an improved accuracy of determining the deterioration of the oxidizing catalyst 13.

Further, the apparatus for deterioration diagnosis according to the present embodiment is designed to determine the deterioration on the basis of the actual cumulative fuel quantity A alone (Step S16), in addition to determining the deterioration on the basis of the ratio between the actual cumulative fuel quantity A and the theoretical cumulative fuel quantity B (Step S14). Thus, even when the ratio between the actual cumulative fuel quantity A and the theoretical cumulative fuel quantity B has a reliability lowered due to error factors such as disturbance, the apparatus for deterioration diagnosis according to the present embodiment can prevent determination error by determining the deterioration on the basis of the actual cumulative fuel quantity A, and achieve an improved accuracy of determining the deterioration of the oxidizing catalyst 13.

In the above, the embodiment has been described. The present invention is, however, not restricted to the described embodiment. For example, although the described embodiment of the present invention is an apparatus for deterioration diagnosis of the oxidizing catalyst 13 used to cause the temperature rise of the DPF 14 for the purpose of forced regeneration of the DPF 14, the application of the oxidizing catalyst 13 is not restricted to this. For example, the oxidizing catalyst 13 may be used for SOx purge of an adsorption-type NOx catalyst provided to purify the exhaust by converting NOx. Specifically, the adsorption-type NOx catalyst experiences so-called sulfur poisoning, which is a phenomenon that SOx (sulfur oxides) adsorbed in place of NOx lowers the exhaust purification performance of the NOx catalyst. Thus, SOx purge, namely purging of SOx adsorbed on the NOx catalyst needs to be performed by providing a oxidizing catalyst 13 upstream of the NOx catalyst, as in the above-described embodiment, to raise the temperature of the NOx catalyst using heat generated in oxidation reaction of unburned fuel. In this case, an apparatus for deterioration diagnosis can be arranged to determine the deterioration of this oxidizing catalyst 13 used for the SOx purge of the NOx catalyst (catalytic device), in the same manner as in the above-described embodiment.

Further, although in the described embodiment, unburned fuel is supplied to the oxidizing catalyst 13 by post-injection, the manner of supplying unburned fuel to the oxidizing catalyst 13 is not restricted to this. For example, it may be arranged such that unburned fuel is supplied by a fuel injection valve fitted to the exhaust passage 11. Also in this case, actual fuel injection quantity (corresponding to actual post-injection quantity) can be determined on the basis of valve open period of the fuel injection valve, and actual cumulative fuel quantity A can be obtained by accumulating the actual fuel injection quantity, successively. Theoretical post-injection quantity and theoretical cumulative fuel quantity B are the same as those in the described embodiment. Thus, on the basis of these actual cumulative fuel quantity A and theoretical cumulative fuel quantity B, the apparatus for the deterioration diagnosis can determine the deterioration of the oxidizing catalyst 13.

Further, in the described embodiment, the ECU 21 determines at Step S16 whether or not the oxidizing catalyst 13 is deteriorated on the basis of the actual cumulative fuel quantity A alone. This step may, however, be omitted, namely, it may be modified such that the ECU 21 determines the deterioration only on the basis of the ratio between the actual cumulative fuel quantity A and the theoretical cumulative fuel quantity B at Step S14.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 

1. An apparatus for deterioration diagnosis of an oxidizing catalyst, comprising: an exhaust purification device disposed in an exhaust passage of an engine for purifying exhaust from the engine; an oxidizing catalyst disposed upstream of the exhaust purification device; unburned fuel supply means for, when temperature rise of the exhaust purification device is required, performing temperature rise control to supply unburned fuel to the oxidizing catalyst to cause temperature rise of the exhaust purification device using heat generated in oxidation reaction of unburned fuel on the oxidizing catalyst; actual cumulative fuel quantity calculation means for obtaining actual cumulative fuel quantity by successively accumulating the amount of unburned fuel supplied to the oxidizing catalyst by the unburned fuel supply means during the temperature rise control; theoretical cumulative fuel quantity calculation means for calculating fuel supply quantity required for temperature rise of the exhaust purification device, on the premise that oxidation performance of the oxidizing catalyst is not deteriorated, and obtaining theoretical cumulative fuel quantity by successively accumulating the calculated fuel supply quantity during the temperature rise control; and deterioration determination means for determining whether or not the oxidizing catalyst is deteriorated, on the basis of the ratio between the actual cumulative fuel quantity obtained by the actual cumulative fuel quantity quantity obtained by the actual cumulative fuel quantity calculation means and the theoretical cumulative fuel quantity obtained by the theoretical cumulative fuel quantity calculation means, after the temperature rise control ends.
 2. The apparatus for deterioration diagnosis of an oxidizing catalyst according to claim 1, wherein the unburned fuel supply means performs the temperature rise control to restore exhaust purification function of the exhaust purification device.
 3. The apparatus for deterioration diagnosis of an oxidizing catalyst according to claim 2, wherein the exhaust purification device is a filter for trapping particulate matter emitted from the engine, and the unburned fuel supply means performs the temperature rise control to burn off the particulate matter trapped by the filter.
 4. The apparatus for deterioration diagnosis of an oxidizing catalyst according to claim 2, wherein the exhaust purification device is a NOx catalyst for converting NOx emitted from the engine, and the unburned fuel supply means performs the temperature rise control to restore exhaust purification function of the NOx catalyst.
 5. The apparatus for deterioration diagnosis of an oxidizing catalyst according to claim 4, wherein the unburned fuel supply means performs the temperature rise control to perform SOx purge of the NOx catalyst.
 6. The apparatus for deterioration diagnosis of an oxidizing catalyst according to claim 1, wherein the unburned fuel supply means supplies unburned fuel to the oxidizing catalyst by performing post-injection in expansion stroke or exhaust stroke after main injection to the engine, and the actual cumulative fuel quantity calculation means obtains the actual cumulative fuel quantity by successively accumulating the amount of unburned fuel supplied to the oxidizing catalyst by the post-injection.
 7. The apparatus for deterioration diagnosis of an oxidizing catalyst according to claim 1, wherein the unburned fuel supply means supplies unburned fuel to the oxidizing catalyst by injecting fuel through a fuel injection valve fitted to the exhaust passage, and the actual cumulative fuel quantity calculation means obtains the actual cumulative fuel quantity by successively accumulating the amount of unburned fuel supplied to the oxidizing catalyst by injection through the fuel injection valve fitted to the exhaust passage.
 8. The apparatus for deterioration diagnosis of an oxidizing catalyst according to claim 1, wherein the theoretical cumulative fuel quantity calculation means obtains the theoretical cumulative fuel quantity by successively accumulating fuel supply quantity calculated on the basis of inlet temperature of the oxidizing catalyst and intake air flow rate of the engine.
 9. The apparatus for deterioration diagnosis of an oxidizing catalyst according to claim 1, wherein the deterioration determination means determines that the oxidizing catalyst is deteriorated, when the ratio between the actual cumulative fuel quantity and the theoretical cumulative fuel quantity exceeds a first threshold value and the actual cumulative fuel quantity exceeds a second threshold value. 